Graphics.fillregion takes too long time

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1.00/5 (1 vote)

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I have 200 Polygons.
Each polygon is made up of thousands of Points.(C#)

public Region GetGraphicsRegion(PointF offsetPoint, float ratioMicron, Graphics gfx = null)
{
Region region = null;

foreach (Polygon polygon in Polygons) // about 20000 Polygons
{
Region subRegion = polygon.GetGraphicsRegion(offsetPoint, ratioMicron, gfx); // polygon is made up of thousands of Points.

if (region == null)
{
region = subRegion;
continue;
}

if (polygon.isHole)
region.Exclude(subRegion);
else
region.Union(subRegion);

subRegion.Dispose();
}

if (gfx != null)
{
if (isPolarity())
gfx.FillRegion(Brushes.Yellow, region); // It takes about 15hours
else
gfx.FillRegion(Brushes.DarkBlue, region);
}

return region;
}

Why is it taking so long?
Is there any way to improve it?

What I have tried:

Is it possible to modify the gfx.FillRegion to get the same result by moving it into the foreach statement?

Posted 25-Mar-21 21:50pm

smbg11

Updated 25-Mar-21 22:44pm

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OriginalGriff · Answer 1 · 2021-03-25T22:44:00

No, probably not.
Look at your data:

20,000 polygons.
Each polygon is "thousands of points".
And you are either excluding or including the region in a composite.

The resulting region is going to be highly complex, and require significant processing to decide if a point is inside or outside - the only way to speed it all up is to simplify the region.

I'd start by finding where the 15 hours is being taken: the Stopwatch class[^] will help you isolate that to either the "build a region" or "draw the region" sections. Personally, I'd guess it's the former rather than the later, but I haven't looked too closely at how Union and Exclude work - it's possible that they defer execution until the Region is used, which could explain why the draw is appearing to be slow.